1. Field of the Invention
The present invention relates to a modified plastic film and, particularly, it relates to a modified plastic film wherein the waving of the whole film caused by heat and waving of film edges caused by moisture are reduced. The present invention further relates to recording materials utilizing such a modified plastic film and, particularly, it relates to recording materials wherein the waving of the whole recording sheet caused by heat and the waving of edges of the recording sheet caused by moisture are reduced when it is used for copying in a plain paper copier (PPC), laser beam printer or the like.
2. Prior Art
Since plastic films are transparent, excellent in chemical resistance, easy to form, inexpensive and sufficiently strong, they have been used as supports in various industrial materials, building materials, materials for decoration, materials for home use and the like, such as second original films, graphic arts films, films for overhead projection, video tapes, audio tapes, floppy discs and photographic films. Such plastic films include polyester films, polycarbonate films, acetylcellulose films, polyvinyl chloride films and the like.
Plastic films used as supports in various recording sheets include plastic films of which both surfaces are laminated to thermosetting recording layers formed from acrylic polyols, isocyanates and, optionally, matting agents, in order to improve solvent resistance of the paper sheets which is required for retouch or correction by various writing materials applied to the sheets.
However, plastic materials generally have a relatively low softening temperature. For example, polyester, which is the most commercially popular plastic material, has a glass transition temperature of about 70.degree. C. and, if a plastic film composed of it is employed for a use where it is heated to a temperature above its glass transition temperature, the film would be softened and hence deformed. Examples of such a use include use as recording sheets such as those for second original films for PPC and films for overhead projectors. When plastic films are used as printing sheets for PPC and the like, the films are deformed due to the temperature employed to fix the toner and in printing they are given a very wavy form as a whole. Such phenomena are particularly remarkable in machines using a high temperature for fixing such as laser beam printers and machines using a long fixing time and, in such machines, the sheets would cause jamming in the sheet transfer route.
Therefore, plastic films can be used for such purposes only in machines using a low fixing temperature and a short fixing time. Laser beam printers and the like, which use a high fixing temperature, cannot use plastic films, but only paper sheets.
Various plastic films are usually cut into sheets and stacked or rolled for their storage. The films stored in the form of stacked sheets or rolled film absorb moisture from their four side edges in the case of stacked sheets and from both ends of the roll in the case of rolled sheets and they exhibit wavy edges (referred as "petal phenomenon" hereinafter) when they are spread or unrolled. The petal phenomenon causes various problems. For example, in the field of photograving, it causes poor contact of photosensitive films upon contact exposure, poor cutting lines for masking films in automatic drawing machines, distortion of cut lines, poor positioning of the sheets and the like. Also in the field of design drafting, such plastic films have various problems such as walk-off, distortion of lines and poor positioning of sheets when drawing with pen plotters on tracing films, sheet jamming when copying second originals by PPC, and poor contact of second originals with photosensitive materials upon contact exposure.
As a method for preventing the petal phenomenon, humidity controlling paper sheets have been interleaved between adjacent films to reduce the influence of outside air humidity. Therefore, the additional process step for interleaving the humidity controlling paper sheets is inevitable and the paper sheets must be pealed off and discarded upon use of the films. These steps make the process troublesome and may cause problems from the viewpoint of resource-saving.
The object of the present invention is to solve the above problems and to provide a modified plastic film less susceptible to waving of the whole film caused by heat and edge waving caused by moisture. A further object of the present invention is to provide a recording material which retains a flat form and does not cause jamming even when used in printers utilizing a high toner fixing temperature such as laser beam printers and in which the petal phenomenon, caused by moisture absorption upon storage, is prevented.